This project continues the development and support of ERPLAB Toolbox, a Matlab-based open source software package for the analysis of event-related potential (ERP) data. ERPs provide information about brain activity related to perception, cognition, emotion, and action with millisecond resolution and are widely used to study a broad range of basic and translational science issues in psychology, neuroscience, psychiatry, neurology, and related fields. There has been an explosion in ERP research, but progress has been hampered by the limited abilities of commercial ERP analysis software and the lack of full-featured open source ERP analysis packages. This situation has slowed the development of new directions in ERP research, instead encouraging researchers to continue with existing approaches supported by the built-in functions of the available ERP analysis packages. ERPLAB Toolbox directly addresses these problems. It merges the functionality of an existing closed source ERP analysis system, ERPSS, with an open source EEG processing package, EEGLAB. EEGLAB provides the EEG processing functions that are the first steps in ERP analysis and a convenient graphical user interface (GUI). ERPLAB builds on EEGLAB by adding powerful tools for the subsequent stages of ERP analysis. All ERPLAB tools can be accessed from the GUI, and they can also be accessed from Matlab scripts to provide automation and customization. ERPLAB will provide powerful but easy-to-use tools for the basic analysis procedures that are commonly used by ERP researchers. It will also provide a set of advanced functions that are either currently in widespread use or are underutilized. This set of basic and advanced functions will greatly improve the quality and decrease the cost of ERP research. In addition, ERPLAB is designed to be easily extended by anyone with rudimentary programming skills. The community of users will therefore contribute to the development of ERPLAB, providing implementations of existing techniques that are very important to various subgroups of ERP researchers and allowing the development and dissemination of new tools that can advance the state of the art. A beta version of ERPLAB is now available, and the goal of the proposed project is to continue the development of the software and to provide the documentation and end-user support that is necessary to maximize the usefulness of the package. Over 500 researchers have already joined our effort, and we anticipate at least 2,000 users by the end of the proposed project period. By providing powerful processing tools to this large set of users, we hope to improve the analysis of data from current experimental paradigms and to help researchers to push the boundaries of science by making it easy for them to develop analysis tools that are not anticipated by current ERP analysis systems.